Spot prevention in light-sensitive silver halide emulsion layers



United States PatentOfifice 3,078,163 Patented Feb. 19, 1963 graphiclayer.

SPOT PREVENIION IN LIGHT-SENSITIVE SILVER HALIDE EIViULSIQI J LAYERS"JozefFrans'Willemsand GerardMichiei Sevens, Wiiriilr- Antwerp;Bel'gium, assign'ors to' GevaertPhoto-Produc- -ten N.V., Mouser-Antwerp,Belgium, a Belgian com- P l 'i'NoiDi-awing. '"Filed Nov. 29,1960; Ser.No. 72,300 Claims rpriority, application" Belgium Dec. 2, 195% 4 Claims.(:96-67) This invention relates to a method for preventing the formationof small spots caused by the presence of heavy -metals and/ or theircompounds. in iphotographic silver halide emulsions.

-Duringrcasting=and further proce'ssing of" photographic i-m-aterial,great difiiculties sometimes: arisenthe causes of which are notalwaysk-nown. r Oneof the maindifficulties is the'dustwhi'ch duringthe-whole cycle of the preparation can set down onto the photographicelement.

Sincedrying the cast photographic layers requires quite a lot ofair-and-since without special precautions this air ispollutedbydust'particlea-itis evidentithat much dust sets down onto-thestill moist and stickycoated' photo- This evil canpractically completelybe remedied by thoroughly filtratingthedrying air so that practicallyall dust'particles are removed. The drying air, however, is not the onlycause of dust. Also the coating machines, the transport machines and thewhole manu- =As a mat-ter of fact, even if precautions are taken inall-manufacturing steps in order to reduce dust'forma- -tion to'anabsolute-minimum, this does not prevent the settling of minimal tracesof dust onto the manufactured material.

The dust itself-has a very complex composition. The most occurringelements are vegetable and animal fibres .suchas paper dustand textilefibres, further soot, sand, ,insects, rustand fine metalparticles.elements do not cause a chemical reaction'on'the photographic emulsionand the particles whichnotwithstand- Some of these ing the extremelycareful precautions mightset down onto the light-sensitivesilverhalide-emulsion, are so sm-alland in solimited a number that theydo-not-cause any visible faults in the finished photographic material.

More harm is done, however, by the chemically active substance which byits secondary reaction with the emulsion enlarges the caused. faults,not visible to the naked eye, and which according to-the nature of thedust and 'theemulsion occasions during processing the exposed materialthe'appearance of small light and .darlcspots. Chernically reactive dustis mainly composed of metal particles or metal compounds among othersmetal oxides, especially of heavy metals such as'iron, copper, tin,lead, chromium and nickel. These metal particles or metal compoundsmainly originate from the construction material of the coating machineryand the working up machines.

Sometimes, however, the-used photochemicals contain traces of thesemetals or'of metal compounds, whilst they can also further be present inthe used supports such as paper, film and glass on which thelight-sensitive emulsions are coated.

' The metal particles can be affected more or less slowly in thephotographic layersand the formed corrosion products:can .difiuse awayfrom the central nucleus.

These corrosion products can exert either a sensitizing or adesensitizing action on the emulsion so that after normal bath treatmentof the photographic element a black spot or a white spot respectively,is formed.

Further, most ofthese metals or their compounds can have a reducingeffect and cause a spontaneous development which leads to small blackspots. Other influences such as affection of the latent image andhindrance of development lead in their turn to small white spots. In allthese cases, the formed small spot is always much larger than the dustparticle' which is the cause of this undesirable phenomenon. This caneasily be checked for instance by bleaching out--thesilver with a usualoxidation meansin the:materialshowing'ablack spot. The black spotsmostly disappear but in the central part remains a very small nucleuswhich is only visible on enlargement.

Also fine metal particles ordust particles consisting of metal compoundswhich are present in a non-light-sensi tive but adjacent layer, exerts apractically same disadvantageous eifect on the superposed or subjacentlight sensitive layer. The harmful "corrosion products of the metalparticles or the dissolved elements of the metal compounds canindeed-reachdnto the light-sensitive layer by diitusiontand causetherein the above mentioned faults.

Wow we have found that the formation of spots in photographic imagescanbe avoided by adding to one or more layers which are used for thecomposition of the photographic material compounds according to one ofthe general formulae ",RyandzR eachrrepresents a member selectedfrom theR represents a member selected' fromthegroupconsist- ,ingof'a'hydrogen'atom, aphenyl group and a p-carboxy phenyl group, and"Rgrepresents. a member selected fromthe group consisting ofwa hydrogenatom and an alkyL group.

Hereinafter follow some examples. 'of suitable com- -pounds:

CHzOH-C O-GH:

Hydroxyactone .CHzOH--CO-CH2OH .Diliydroxyacetone HO CH='GOH-OHOTriosereductone Hail-+0 O.CHC O 0 02110 C O CH;

a-JAeetoxyacetyl acetic acid ethyl ester 'HO 0 0-0 OH=C OH0.0 0H

Dihydroxymaleic acid HaCOO-'-CHOH-'GH .3-113 droxy-Z-butanone (oraeetoin) H7C3'COCHOH.O3H7 5-hydroxy-4-octanone (orhutyroin) OsH-CO-OHiOH w Hydroxyacetophenone l N ll N HO HOH;,1-phenyl-3-methyl-4,5-dihydroxypyrazole COOH l HOJN\N slats,

1-(p-carboxyphenyl)-3-methyl-4,5-dihydroxypyrazole 3 nojl N H CH33-methyl-4,5-dihydroxypyrazole The compounds according to the presentinvention can be added in different amounts to the emulsions accordingto the compounds chosen, the nature of the colloid binding agent for thesilver halide grains and the amount and the nature of the silver halideused. Amounts of 0.5 to 2.5 g. per 10 g. of silver metal present in theemulsion as silver halide are preferably used although larger amountsmay be added in case it might become necessary. They can, moreover,successfully be added to other layers than the light-sensitive layerssuch as for instance to a protective layer, an intermediate layer or abarytacoating.

Evidently, the method according to the present invention can be appliedfor the manufacture of photographic light-sensitive film as Well as ofphotographic paper.

The use of these compounds for counteracting the formation of spots inphotographic images has the advantage of not being accompanied by anyharmful secondary effect. On the contrary, some of these compounds whenadded to a silver chloro-bromide emulsion, increase to some extent thegeneral light-sensitivity of this emulsion without noxious influence onthe photographic properties pursued, such as for instance fog andstability.

A further advantage is that the compounds according to the presentinvention are well compatible with the other emulsion additives such asfor instance dispersing agents, color couplers, surface-activecompounds, optical bleaching agents, anti-oxidizing agents, sensitizers,antifogging agents, stabilizers, hardeners or plasticizers, etc.

The present invention is illustrated by the following examples withoutlimiting, however, the scope thereof.

Example 1 Part of a flowable silver chloro-bromide emulsion with pH 4.5(about 20% of silver bromide) for being applied to paper base is coatedonto a strip of baryta-coated paper soiled with metal dust (test stripA); to another part of this emulsion 20 cm. of a 5% alcoholic solutionof alphaacetoxy-acetyl acetic acid ester are added per kg. of emulsionand this second part of emulsion is coated onto a second strip of thesame baryta-coated paper (test strip B); to a third part of thisemulsion 20 cm. of a 5% alcoholic solution of triosereductone are addedper kg. of emulsion whereafter also this third emulsion part is coatedonto a third strip of the same baryta-coated paper (test strip C).

These three test strips are dried and exposed in such a way that afterdevelopment a density of 0.6 is attained. After development, it appearsthat test strip A shows numerous small black spots having a densitywhich is considerably higher than 0.6. This is not the case for the teststrips B and C. Moreover, an increase of sensitivity of 20% has beenobserved on test strip C, without further influence on the gradation andother photographic characteristics.

Example 2 Part of a warm-tone silver chlorobromide emulsion with pH 4.7(about 30% of silver bromide) for being applied onto paper base iscoated onto a strip of barytacoated paper soiled with metal dust (teststrip A); part of this material is provided with an antistress layermainly composed of gelatin. To the usual coating composition from whichthis antistress layer is coated 2S cm. of a 5% alcoholic solution of3-methyl-4,S-dihydroxypyrazole were added per litre (test strip B);another part of this paper is likewise coated with the same antistresslayer not containing however 3-methyl-4,5-dihydroxypyrazole (test stripC). After exposure and development to low densit the test strip B doesnot show black spots, whereas the test strips A and C show many smallblack spots.

Example 3 A strip of a paper support with metal dust is provided with agelatin precoat containing an antihalation sub stance (test strip A); toa second strip of the same paper support likewise soiled with metal dusta gelatin precoat is applied from a coating solution which, however,besides the same antihalation substance as in strip A, 40 cm. of a 5%alcoholic solution of 1-phenyl-3-methyl-4,5-dihydroxypyrazole were addedper 1 litre of coating solution (test strip B); to a third strip of thesame paper support a gelatin precoat is applied from a coating solutionto which, however, besides the same antihalation substance as in stripA, 20 cm. of a 5% alcoholic solution of l-pcarboxyphenyl-3methyl-4,5dihydroxypyrazole per litre of coating solution were added.

On the precoat of each test strip is coated the same silver-chlorideemulsion with pH 5', suitable for the preparation of aluminum offsetsheets such as described in the U.S. patent application Serial No.846,256, filed October 14, 1959.

Contrary to test strip A, the test strips B and C after exposure anddevelopment show a homogeneous density without black spots.

We claim:

1. A photographic material comprising a support and at least one layersuperposed thereon, one such layer being a light-sensitive silver halideemulsion layer, said material being characterized in that at least oneof the layers thereof contains a compound having a formula selected fromthe group consisting of:

HOj no I la.

wherein carbethoxy group, a phenyl group and a furyl group; R representsa member selected from the group consisting of a hydrogen atom and anacetyl group, and R represents a member selected from the groupconsisting of a hydrogen atom, a phenyl group and a p-carboxy phenylgroup, whereby the formation in said emulsion layer spots caused by dustsuch as metallic particles and the like is substantially in hibited. 2.A photographic material having a light-sensitive silver halide emulsionlayer containing alpha-acetoxyacetyl acetic acid ethyl ester.

3. A photographic material having a light-sensitive silver halideemulsion layer and an antistress layer containing3methyl-4,S-dihydroxypyrazole.

4. A photographic material having a light-sensitive silver halideemulsion layer and a gelatin precoat containing 1(p-carboxyphenyl)-3-methyl4,5-dihydroxypyrazole.

References Cited in the file of this patent UNITED STATES PATENTS2,346,095 Weissberger et a1 Apr. 4, 1944

1. A PHOTOGRAPHIC MATERIAL COMPRISING A SUPPORT AND AT LEAST ONE LAYERSUPERPOSED THEREON, ONE SUCH LAYER BEING A LIGHT-SENSITIVE SILVER HALIDEEMULSION LAYER, SAID MATERIAL BEING CHARACTERIZED IN THAT AT LEAST ONEOF THE LAYERS THEREOF CONTAINS A COMPOUND HAVING A FORMULA SELECTED FROMTHE GROUP CONSISTING OF: